The present invention relates generally to implantable medical devices such as pacemakers and more particularly to a method and apparatus to acquire electrocardiographic data, waveform tracings, and other physiologic data displayable by a programmer from an implantable medical device patient without the need for, or use of, surface (skin) contacting electrodes.
The electrocardiogram (ECG) is commonly used in medicine to determine the status of the electrical conduction system of the human heart. As practiced the ECG recording device is commonly attached to the patient via ECG leads connected to pads arrayed on the patient""s body so as to generate a recording that displays the cardiac waveforms in any one of 12 possible vectors.
The history of the ECG dates back to 1842 when the Italian physicist, Carlo Matteucci discovered that each heartbeat was accompanied by a detectable electric signal. In 1878, two British physiologists, John Burden Sanderson and Frederick Page, determined that the heart signal consisted of, at least, two phases, the QRS (ventricular depolarization) and the repolarization or T-wave. It was not until 1893, however, that Willem Einthoven introduced the term xe2x80x98electrocardiogramxe2x80x99 at a meeting of the Dutch Medical Association, although he later disavowed he was the originator of the term.
Einthoven may, however, be called the father of electrocardiography, since he won the Nobel Prize for his achievements in 1924. It was he who finally dissected a heart and named all of the cardiac waveforms (P, Q, R, S, T) that commonly appear on an ECG tracing from a xe2x80x98normalxe2x80x99 person.
Einthoven and other medical practitioners of that time were aware of only three vectors (I, II, and III) that are achieved by placement of the ECG electrodes on specific body sites. The remaining nine sites were discovered later in the twentieth century. In 1938, American Heart Association and the Cardiac Society of Great Britain defined the standard positions (I-III) and wiring of the chest leads V1-V6. The xe2x80x98Vxe2x80x99 stands for voltage. Finally, in 1942, Emanuel Goldberger added the augmented limb leads aVR, aVL and aVF to Einthoven""s three limb leads and the six chest leads thereby creating the 12-lead electrocardiogram that is routinely used today for cardiac diagnostic purposes.
Since the implantation of the first cardiac pacemaker, implantable medical device technology has advanced with the development of sophisticated, programmable cardiac pacemakers, pacemaker-cardioverter-defibrillator arrhythmia control devices and drug administration devices designed to detect arrhythmias and apply appropriate therapies. The detection and discrimination between various arrhythmic episodes in order to trigger the delivery of an appropriate therapy is of considerable interest. Prescription for implantation and programming of the implanted device are based on the analysis of the PQRST electrocardiogram (ECG) that currently requires externally attached electrodes and the electrogram (EGM) that requires implanted pacing leads. The waveforms are usually separated for such analysis into the P-wave and R-wave in systems that are designed to detect the depolarization of the atrium and ventricle respectively. Such systems employ detection of the occurrence of the P-wave and R-wave, analysis of the rate, regularity, and onset of variations in the rate of recurrence of the P-wave and R-wave, the morphology of the P-wave and R-wave and the direction of propagation of the depolarization represented by the P-wave and R-wave in the heart. The detection, analysis and storage of such EGM data within implanted medical devices are well known in the art. Acquisition and use of ECG tracing(s), on the other hand, has generally been limited to the use of an external ECG recording machine attached to the patient via surface electrodes of one sort or another.
The aforementioned ECG systems that utilize detection and analysis of the PQRST complex are all dependent upon the spatial orientation and number of electrodes available in or around the heart to pick up the depolarization wave front.
As the functional sophistication and complexity of implantable medical device systems increased over the years, it has become increasingly more important for such systems to include a system for facilitating communication between one implanted device and another implanted device and/or an external device, for example, a programming console, monitoring system, or the like. For diagnostic purposes, it is desirable that the implanted device be able to communicate information regarding the device""s operational status and the patient""s condition to the physician or clinician. State of the art implantable devices are available that transmit a digitized electrical signal to display electrical cardiac activity (e.g., an ECG, EGM, or the like) for storage and/or analysis by an external device. The surface ECG, in fact, has remained the standard diagnostic tool since the very beginning of pacing and remains so today.
To diagnose and measure cardiac events, the cardiologist has several tools from which to choose. Such tools include twelve-lead electrocardiograms, exercise stress electrocardiograms, Holter monitoring, radioisotope imaging, coronary angiography, myocardial biopsy, and blood serum enzyme tests. Of these, the twelve-lead electrocardiogram (ECG) is generally the first procedure used to determine cardiac status prior to implanting a pacing system; thereafter, the physician will normally use an ECG available through the programmer to check the pacemaker""s efficacy after implantation. Such ECG tracings are placed into the patient""s records and used for comparison to more recent tracings. It must be noted, however, that whenever an ECG recording is required (whether through a direct connection to an ECG recording device or to a pacemaker programmer), external electrodes and leads must be used.
Another possible approach is described in pending applications Ser. No. 09/749,169, Leadless Fully Automatic Pacemaker Follow-Up filed Dec. 27, 2000; Ser. No. 09/696,365, Multilayer Ceramic Electrodes For Sensing Cardiac Depolarization Signals, filed Oct. 25, 2000; Ser. No. 09/697,438, Surround Shroud Connector and Electrode Housings For A Subcutaneous Electrode Array and Leadless ECGs, filed Oct. 26, 2000; Ser. No. 09/703,152, Subcutaneous Spiral Electrode For Sensing Electrical Signals of the Heart, filed Oct. 31, 2000; Ser. No. 09/736,640, Atrial Aware VVIxe2x80x94A Method For Atrial Synchronous Ventricular (VDD/R) Pacing Using the Subcutaneous Electrode Array and a Standard Pacing Lead, filed Dec. 14, 2000; Ser. No. 09/850,331, Subcutaneous Sensing Feedthrough/ Electrode Assembly, filed May 7, 2000; and Ser. No. 09/721,275, System And Method For Deriving a Virtual ECG IR EGM Signal, filed Nov. 22, 2000; whereby a subcutaneous leadless pseudo EKG is sensed from the can of the IMD and transmitted to an external programmer via telemetry. The ""169, ""365, ""438, ""152, ""640, ""331, and ""275 applications are incorporated herein by reference in their entireties.
In the art known to the inventors and current practice there are noticeable limitations. For example, electrocardiogram analysis performed using existing external or body surface ECG systems can be limited by mechanical problems and poor signal quality. Electrodes attached externally to the body are a major source of signal quality problems and analysis errors because of susceptibility to interference such as muscle noise, power line interference, high frequency communication equipment interference, and baseline shift from respiration or motion. Signal degradation also occurs due to contact problems, ECG waveform artifacts, and patient discomfort. Externally attached electrodes are subject to motion artifacts from positional changes and the relative displacement between the skin and the electrodes. Furthermore, external electrodes require special skin preparation to ensure adequate electrical contact. Such preparation, along with positioning the electrode and attachment of the ECG lead to the electrode needlessly prolongs the pacemaker follow-up session.
Other art relating to subcutaneous leadless pseudo EKG concept deals with generating a pseudo EKG signal via pulse generator externalized electrodes and signal conditioning electronics. This method of EKG acquisition is rapid, does not require electrode positioning and does not require patient disrobing. However, there is substantial increase in device cost, increased circuit complexity, increased IMD device size, and an IMD aesthetic degradation.
Prior art describes systems to monitor electrical activity of the human heart for diagnostic and related medical purposes. U.S. Pat. No. 4,023,565 issued to Ohlsson describes circuitry for recording ECG signals from multiple lead inputs. Similarly, U.S. Pat. No. 4,263,919 issued to Levin, U.S. Pat. No. 4,170,227 issued to Feldman, et al, and U.S. Pat. No. 4,593,702 issued to Kepski, et al, describe multiple electrode systems which combine surface EKG signals for artifact rejection.
The primary implementation for multiple electrode systems in the prior art is vector cardiography from ECG signals taken from multiple chest and limb electrodes. This is a technique whereby the direction of depolarization of the heart is monitored, as well as the amplitude, generally similar to the disclosure in U.S. Pat. No. 4,121,576 to Greensite.
Numerous body surface ECG monitoring electrode systems have been employed in the past in detecting the ECG and conducting vector cardiographic studies. For example, U.S. Pat. No. 4,082,086 to Page, et al., discloses a four electrode orthogonal array that may be applied to the patient""s skin both for convenience and to ensure the precise orientation of one electrode to the other. U.S. Pat. No. 3,983,867 to Case describes a vector cardiography system employing ECG electrodes disposed on the patient in normal locations and a hex axial reference system orthogonal display for displaying ECG signals of voltage versus time generated across sampled bipolar electrode pairs.
U.S. Pat. No. 4,310,000 to Lindemans and U.S. Pat. Nos. 4,729,376 and 4,674,508 to DeCote, incorporated herein by reference, disclose the use of a separate passive sensing reference electrode mounted on the pacemaker connector block or otherwise insulated from the pacemaker case in order to provide a sensing reference electrode which is not part of the stimulation reference electrode and thus does not have residual after-potentials at its surface following delivery of a stimulation pulse.
Moreover, in regard to subcutaneously implanted EGM electrodes, the aforementioned Lindemans U.S. Pat. No. 4,310,000 discloses one or more reference-sensing electrode positioned on the surface of the pacemaker case as described above. U.S. Pat. No. 4,313,443 issued to Lund describes a subcutaneously implanted electrode or electrodes for use in monitoring the ECG.
Finally, U.S. Pat. No. 5,331,966 to Bennett, incorporated herein by reference, discloses a method and apparatus for providing an enhanced capability of detecting and gathering electrical cardiac signals via an array of relatively closely spaced subcutaneous electrodes (located on the body of an implanted device).
The present invention encompasses a non-tissue contacting electrode system for the sensing of physiologic signals from a patient that may be implemented during the implant and/or follow-up of an implantable medical device (IMD) via an external programmer or other monitoring instrument. These sensing systems are electrically connected to the circuitry of the external device and detect cardiac depolarization waveforms displayable as electrocardiographic tracings on the instrument screen when the programming head is positioned above an implanted device, such as a pacemaker, so equipped with a non-tissue contacting electrode system.
The present invention provides a method and apparatus that may be implemented for use in conjunction with the aforementioned medical devices to provide an enhanced capability of detecting and gathering electrical cardiac signals via non-tissue contacting sensors.
The present invention enables the physician or medical technician to perform follow-up regiments that, in turn, eliminate the time it takes to attach external adhesive electrodes to the patient""s skin. Such timesavings can reduce the cost of follow-up, as well as making it possible for the physician or medical technician to see more patients during each day. Though not limited to these, other uses include: Holter monitoring with event storage, arrhythmia detection and monitoring, capture detection, ischemia detection and monitoring (S-T elevation and depression on the ECG), changes in QT interval (i.e., QT variability), transtelephonic monitoring, web-enabled remote patient management and chronic remote patient care.